1. Field of the Invention
This invention relates to a glass base material, which is a base material of an optical fiber, manufacturing apparatus and a glass base material manufacturing method.
2. Description of the Related Art
There are several processes involved in the manufacture of an optical fiber. A gas material, which is a base material of an optical fiber, is hydrolyzed and formed into a glass base material. The glass base material is sintered to form an optical fiber preform, which is drawn to form an optical fiber.
There are several methods for manufacturing a glass base material. As one of the methods for manufacturing a glass base material, there is an OVD method, that is, an outside vapor deposition method. In the OVD method, a gas material is hydrolyzed by a burner to form glass particles which form the base material of the optical fiber. The glass particles are accumulated around and along a base rod, which is rotated at a constant speed, and the accumulated glass particles become a glass base material.
To increase the productivity of manufacture of glass base materials, a plurality of burners are used for hydrolyzing the gas material. The plurality of burners are moved back and forth along the longitudinal direction of the base rod, in order to form a glass base material having a constant diameter. The turning point of the back and forth movement of the burners needs to be dispersed evenly along the longitudinal direction of the base rod, so that the diameter of the glass base material accumulated by the burners can be constant for substantially the whole length of the glass base material.
There is a method of controlling the position of the turning point by using software that calculates the position of the turning point of the burners. To control the turning point to be a predetermined position, several steps have to be executed.
However, the method of controlling the turning points using software causes a delay in the movement of burners, because it takes time for the software to calculate the turning point and also takes time to provide the calculated turning points to the unit that moves the burners. The burners pass over the turning point which is to be calculated by the software and provided to the unit which moves the burners. Therefore, the diameter of the glass base material becomes uneven and the roughness of the surface of the glass base material increases. Therefore, the quality of the glass fiber drawn from the glass base material having an uneven diameter, decreases.